Solvent and catalyst recovery and recycle in the manufacture of phenoxybenzoic acid derivatives

ABSTRACT

An improved process is provided for recovering and recycling reaction medium solvent and cobalt-containing cocatalyst in the oxidation of 3-(substituted phenoxy) toluene to provide the corresponding 3-(substituted phenoxy) benzoic acid, the latter being a useful intermediate in the manufacture of herbicides such as acifluorfen.

This is a continuation of co-pending application Ser. No. 518,975 filedAug. 2, 1983 now U.S. Pat. No. 4,456,767, which is a continuation of ofU.S. Serial No. 286,942 filed July 27, 1982 now abandoned.

CROSS REFERENCE TO RELATED APPLICATIONS

This application discloses subject matter disclosed in commonlyassigned, co-pending U.S. patent application Ser. No. 208,081 filed Nov.18, 1980 as a continuation-in-part of U.S. patent application Ser. No.067,508 filed Aug. 17, 1979, now abandoned, which in turn is acontinuation-in-part of U.S. patent application Ser. No. 051,254, filedJune 22, 1979, also abandoned. The disclosure of each of the aforesaidpatent applications is incorporated by reference herein.

BACKGROUND OF THE INVENTION

This invention concerns a process for preparing phenoxybenzoic acidderivatives which are useful as herbicides, and in particular,acifluorfen, i.e., the compound5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid, which inthe form of its sodium salt is commercially available as the productTackle (Mobil Oil Corporation). Acifluorfen, which possesses thestructure ##STR1## and related phenoxybenzoic acid derivativesconstitute a class of highly effective herbicides for the post-emergencecontrol of a variety of weeds such as certain broadleafs associated withsoybeans.

Copending U.S. patent application Ser. No. 208,081 filed Nov. 18, 1980and its predecessor applications Ser. Nos. 067,508, filed Aug. 17, 1979and 051,254, filed June 22, 1979, both now abandoned) each describes afour-step synthesis of a class of phenoxybenzoic acid derivatives towhich acifluorfen belongs. The sequence of steps comprising thissynthesis is as follows: ##STR2##

M is an alkali metal atom or ammonium ion. ##STR3## X₁, X₂ and X₃ eachis H, F, Cl, Br, CF₃, OCF₂ CHZ₂ (Z═Cl, F or Br), OCF₃, CN, CO₂ R(R=lower alkyl), --C₆ H₅, O-alkyl, NO₂ or SO₂ (lower) alkyl and is F, Clor Br, provided that at least one of X₁, X₂ and X₃ is other than H.##STR4##

The carboxyl group in the product compounds can be made to undergotransformation to a variety of other groups, including salts, employingconventional procedures.

In oxidation step 3, the catalyst system comprises a source of cobaltcompound and a source of bromide, compound, e.g., a combination ofcobaltous acetate tetrahydrate and sodium bromide. The oxidation iscarried out in a suitable inert solvent, e.g., any of the loweraliphatic carboxylic acids such as acetic acid, and in the presence of afree radical initiator, e.g., any of the peroxides such as hydrogenperoxide. Favorable process economics require an efficient system forcatalyst and solvent recovery in this step. In accordance with therecycle procedures of the aforesaid U.S. patent applications, the cobaltcompound and part of the bromide compound can be recovered and recycledby crystallizing the phenoxybenzoic acid derivative from the reactionsolution, collecting the crystallized product on a basket centrifuge andrecycling the mother liquors which contain the catalyst solvent and afew weight percent of phenoxybenzoic acid derivative to the oxidationstep. The water of reaction can be removed from the recycled motherliquors by conventional means, e.g., fractional distillation or additionof acetic anhydride. The water is advantageously equal to or less than 1weight percent in the recycled mother liquors and equal to or less than2 weight percent after the addition of aqueous peroxide. The catalystand acetic acid remaining on the phenoxybenzoic acid filter-cake can berecovered by dissolving the filter-cake in a suitable solvent such asmethylene chloride and extracting this solution with water. The aceticacid, cobalt acetate, and sodium bromide partition into the aqueousphase which can then be added to the recycled mother liquors.Approximately 88 weight percent of the acetic acid and more than 95weight percent of the cobalt and bromide are recovered in each recycleemploying the foregoing procedures.

SUMMARY OF THE INVENTION

In accordance with the present invention, a process is provided forrecovering and recycling solvent in the oxidation of a phenoxytoluenederivative to provide a phenoxybenzoic acid intermediate which issimpler than the solvent recovery and recycle procedures described inthe U.S. patent applications referred to supra, and therefore representsan improvement over the latter.

Broadly defined, the invention herein is directed to a process forrecovering and recycling solvent in the oxidation of a 3-(substitutedphenoxy) toluene feed to the corresponding 3-(substituted phenoxy)benzoic acid employing a combination of a cobalt compound and a bromidecompound as catalyst which comprises:

(a) distilling a first solvent from the oxidation reaction mixturecontaining 3-(substituted phenoxy) benzoic acid and cobalt compound;

(b) combining solvent-depleted reaction mixture from (a) with a secondsolvent which dissolves 3-(substituted phenoxy) benzoic acid and iscapable of forming an immiscible layer with an aqueous solution of loweraliphatic carboxylic acid;

(c) combining solution of 3-(substituted phenoxy) benzoic acid from (b)with an aqueous solution of lower aliphatic carboxylic acid whichdissolves the cobalt compound to extract cobalt compound from saidsolution;

(d) separating the solution layer of 3-(substituted phenoxy) benzoicacid from the aqueous solution layer of lower aliphatic carboxylic acidand dissolved cobalt compound;

(e) separating aqueous solution of lower aliphatic carboxylic acid fromextracted cobalt compound resulting from step (c) and (d);

(f) recycling the first solvent recovered from (a) to serve as solventin the oxidation of an additional quantity of 3-(substituted phenoxy)toluene feed.

In contrast to the five unit operations required by the solvent andcatalyst recovery process of the aforestated U.S. patent applications,the process of this invention requires only three unit operations with aconsequent significant savings in plant construction and operatingcosts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of one embodiment of the present invention;

FIG. 2 is a graph showing the relationship between weight percent waterremoved and weight percent volatiles in the distillation step (a) of theinvention; and,

FIG. 3 is a graph showing the relationship between weight percent cobaltrecovery and weight percent fraction of methylene chloride (MeCl₂) instep (c) of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, a flow diagram illustrates one embodiment of the presentinvention as applied to the manufacture of a 3-(substituted phenoxy)benzoic acid intermediate i.e.,5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-benzoic acid, which, whennitrated, provides the herbicide acifluorfen. The oxidation step whichis carried out in unit 10 employs oxygen supplied through line 11 as airas the oxidizing agent, recycled acetic acid supplied through line 12 asthe solvent, recycled cobaltous acetate tetrahydrate supplied throughline 13 and sodium bromide supplied through line 14 as the cocatalystsand hydrogen peroxide as the free radical initiator. The oxidationmixture is transferred from oxidation unit 10 through line 15 to aceticacid flash distillation unit 16. The acetic acid is recovered and wateris removed therefrom by taking two cuts in a flash distillation of thevolatile components from the oxidation reaction. The first cut providesthe means for removing water from the system, and this cut is sent toaqueous waste. The second cut from the flash distillation contains theremainder of the water and acetic acid and is made anhydrous by theaddition of acetic anhydride with the glacial acetic acid being recycledto the next oxidation batch through line 12. The optimum point at whichthe first cut is made is based upon economic and material balanceconsiderations. The data shown in FIG. 2 (generated on a laboratoryscale) shows the percent water recovered vs the percent volatiles (waterplus acetic acid) present in the oxidation solution. A typical oxidationsolution contains about 4-8wt% water at the end of the reaction, andusing FIG. 2, it is seen that about 30% of the volatiles must be flashdistilled in order to remove about 60% of the water present. The aceticacid-depleted reaction product from unit 16 is transferred through line17 to dissolving and extraction unit 18 where it is combined with asolvent for the product phenoxybenzoic acid intermediate such asmethylene chloride supplied through line 19 (e.g., 2.67 lbs of methylenechloride per lb of crude phenoxybenzoic acid intermediate) and anaqueous lower aliphatic carboxylic acid such as acetic acid suppliedthrough line 20 (e.g., 0.75 lb of 10% aqueous acetic acid per lb ofcrude phenoxybenzoic acid intermediate) to extract the cobaltous acetatetetrahydrate from the methylene chloride solution. The mixture of thedissolved intermediate, cobaltous acetate tetrahydrate and dilute aceticacid is agitated and heated to 60° C. under a slight pressure (18 psig).Extraction is effected at elevated temperature and slight pressure(e.g., 60° C., at 18 psig) to assure that all of the phenoxybenzoic acidintermediate remains in solution. Approximately 92-93% of the cobalt isrecovered in the aqueous phase. The partitioning of the cobalt into theaqueous phase becomes less favorable as the amount of methylene chorideis decreased (see FIG. 3). The methylene chloride layer (lower phase) isseparated through line 21, mixed with acetic anhydride and stored forthe subsequent nitration step to provide acifluorfen.

The upper aqueous acetic acid solution of cobaltous acetate tetrahydrateis passed through line 22 with the acetic acid being separated from thecobalt compound in flash evaporation unit 23 at atmospheric pressurewith 3-(substituted phenoxy)toluene feed supplied through line 24 actingas a heat transfer medium and steam being released through line 25. Nodecomposition of the aforesaid phenoxytoluene intermediate was observedduring the flash distillation and the cobalt compound appeared to bedissolved in this fluid. A negligible amount of the phenoxy tolueneintermediate was lost by steam-distillation to the aqueous condensate.Cobaltous acetate tetrahydrate recovered from flash evaporation unit 23is recycled to oxidation unit through line 13.

Approximately 95% of the bromide cocatalyst was lost during theoxidation and the acetic acid flash distillations and had to bereplenished before effecting oxidation of a further quantity of startingcompound. Thus, after completing the flash distillation of the water,sodium bromide (0.019 lb per lb of starting compound) was added alongwith the oxidation solvent, glacial acetic acid (2.5 lb per lb ofstarting compound) and free radical initiator (0.075 lb of 30% aqueoushydrogen peroxide) per lb of starting compound. Oxidation using therecycled cobalt compound proceeded smoothly. The previously describedoxidation reaction solution was heated to 90° C., agitated well, andsparged with air. The reaction was 70% complete in 4.5 hrs which is theexpected rate under these conditions.

What is claimed is:
 1. A process for recovering and recycling solvent inthe oxidation of a 3-(substituted phenoxy) toluene feed to thecorresponding 3-(substituted phenoxy) benzoic acid employing acombination of a cobalt compound and a bromide compound as catalystwhich comprises:(a) distilling a first solvent from the oxidationreaction mixture containing 3-(substituted phenoxy)benzoic acid andcobalt compound; (b) combining solvent-depleted reaction mixture from(a) with a second solvent which dissolves the 3-(substitutedphenoxy)benzoic acid and is capable of forming an immiscible layer withan aqueous solution of lower aliphatic carboxylic acid; (c) combiningsolution of 3-(substituted phenoxy)benzoic acid from (b) with an aqueoussolution of lower aliphatic carboxylic acid which dissolves the cobaltcompound to extract the cobalt compound from the solution; (d)separating the solution layer of 3-(substituted phenoxy)benzoic acidfrom the aqueous solution layer of lower aliphatic carboxylic acid anddissolved cobalt compound; (e) separating the aqueous solution of loweraliphatic carboxylic acid from extracted cobalt compound resulting fromsteps (c) and (d); and (f) recycling the first solvent recovered from(a) to serve as solvent in the oxidation of an additional quantity of3-(substituted phenoxy)toluene feed.
 2. The process of claim 1 in whichthe solvent in step (a) is acetic acid.
 3. The process of claim 1 inwhich the cobalt compound is cobaltous acetate tetrahydrate.
 4. Theprocess of claim 1 in which the bromide compound is sodium bromide. 5.The process of claim 1 in which the 3-(substituted phenoxy)toluenestarting compound has the structure ##STR5##5-[2-chloro-4-(trifluoromethyl)phenoxy]toluene and the product compoundhas the structure ##STR6##5-[2-chloro-4-(trifluoromethyl)phenoxy]benzoic acid.
 6. The process ofclaim 2 in which distillation step (a) is effected in two cuts, thefirst cut removing water and the second cut removing aqueous aceticacid.
 7. The process of claim 1 in which the solvent for 3-(substitutedphenoxy)benzoic acid is methylene chloride.
 8. The process of claim 1 inwhich the lower aliphatic carboxylic acid of step (c) is acetic acid. 9.The process of claim 1 in which acetic acid is the solvent used in step(a) and step (d) is carried out by flash distillation of said aceticacid.
 10. The process of claim 5 in which step (d) is carried out byflash distillation of said acetic acid and5-[2-chloro-4-(trifluoromethyl)phenoxy]toluene is employed as heatexchange medium in said flash distillation.
 11. The process of claim 2wherein the second solvent is methylene chloride and the aqueoussolution of lower carboxylic acid from step (c) is an acetic acidsolution.
 12. The process of claim 11 wherein the methylenechloride/3-(substituted phenoxy)benzoic acid solution and the aqueoussolution of lower aliphatic carboxylic/dissolved cobalt compoundsolution form immiscible lower and upper layers, respectively tofacilitate their separation in step (d).
 13. A process for recoveringand recycling solvent in the oxidation of a 3-(substitutedphenoxy)toluene feed to the corresponding 3-(substituted phenoxy)benzoicacid employing a combination of a cobalt compound and a bromide compoundas catalyst which comprises:(a) distilling a first solvent from theoxidation reaction mixture containing 3-(substituted phenoxy)benzoicacid and cobalt compound; (b) combining solvent-depleted reactionmixture from (a) with a second solvent which dissolves the3-(substituted phenoxy)benzoic acid and is capable of forming animmiscible layer with an aqueous solution of lower aliphatic carboxylicacid; (c) combining solution of 3-(substituted phenoxy)benzoic acid from(b) with an aqueous solution of lower aliphatic carboxylic acid whichdissolves the cobalt compound to extract the cobalt compound from thesolution; (d) separating the solution layer of 3-(substitutedphenoxy)benzoic acid from the aqueous solution layer of lower aliphaticcarboxylic acid and dissolved cobalt compound; and (e) separatingaqueous solution of lower aliphatic carboxylic acid from extractedcobalt compound resulting from step (c).
 14. The process of claim 13 inwhich the solvent in step (a) is acetic acid.
 15. The process of claim13 in which the solvent for 3-(substituted phenoxy)benzoic acid ismethylene chloride.
 16. The process of claim 14 wherein the secondsolvent is methylene chloride and the aqueous solution of lowercarboxylic acid from step (c) is an acetic acid solution.
 17. Theprocess of claim 16 wherein the methylene chloride 3-(substitutedphenoxy)benzoic acid solution and the aqueous solution of loweraliphatic carboxylic-dissolved cobalt compound solution form immisciblelower and upper layers, respectively to facilitate their separation instep (d).
 18. A process for recovering and recycling solvent in theoxidation of a 3-(substituted phenoxy)toluene feed to the corresponding3-(substituted phenoxy)benzoic acid employing a combination of a cobaltcompound and a bromide compound as catalyst which comprises:(a)distilling an acetic acid solvent from the oxidation reaction mixturecontaining 3-(substituted phenoxy)benzoic acid and cobalt compound; (b)combining solvent-depleted reaction mixture from (a) with methylenechloride solvent which dissolves the 3-(substituted phenoxy)benzoicacid; (c) combining methylene chloride solution of 3-(substitutedphenoxy)benzoic acid from (b) with an aqueous solution of acetic acidwhich dissolves the cobalt compound to extract the cobalt compound fromthe solution wherein the methylene chloride and acetic acid solutionsform immiscible lower and upper layers respectively; (d) separating thelower layer solution of 3-(substituted phenoxy)benzoic acid from theupper layer aqueous solution of lower aliphatic carboxylic acid anddissolved cobalt compound; and (e) separating the aqueous acetic acidsolution from the extracted cobalt compound resulting from step (c). 19.The process of claim 18 wherein the cobalt compound is cobaltous acetatetetrahydrate and the bromide compound is sodium bromide.